ser ‧ o ‧ to ‧ nin /ˌserəˈtəʊnɪn $ -ˈtoʊ-/ BrE AmE noun [uncountable] technical
[ Date: 1900-2000 ; Origin: serum + tonic + -in ]
a chemical in the body that helps carry messages from the brain and is believed to make you feel happy
ser ‧ o ‧ to ‧ nin /ˌserəˈtəʊnɪn $ -ˈtoʊ-/ BrE AmE noun [uncountable] technical
[ Date: 1900-2000 ; Origin: serum + tonic + -in ]
a chemical in the body that helps carry messages from the brain and is believed to make you feel happy
Longman Dictionary of Contemporary English. Longman - Словарь современного английского языка. 2012